California Agriculture

In recent decades, air quality has improved near most cities but not in rural areas such as the San Joaquin Valley. Many studies using diverse exposure techniques have shown that ground-level ozone air pollution reduces plant growth and yield, from negligible impacts in some species to over 30% losses in others. We studied the interaction of ozone with weed competition from yellow nutsedge in Pima cotton and tomato in open-top field-exposure chambers at the UC Kearney Research and Extension Center in Fresno County. Ozone impacts on cotton (which is relatively sensitive) were compounded by weed competition, whereas tomato (which is less sensitive) competed well at all ozone concentrations. Our data suggests that crop-loss estimates obtained in single-factor experiments accurately reflect the serious risk of ozone to agriculture, but that more accurate yield predictions will require the consideration of interactions between the components of complex crop production systems, including weed competition.